Conventional practice for removing chlorine disinfectant from chlorinated potable water calls for the filtration of water through a filter bed, usually activated carbon or charcoal. In this process the water sample is required to make intimate and relatively extended contact with the filter medium. In addition, a filtration process has a number of physical requirements which make it best suited for application to dedicated, stand-alone appliances for the production of chlorine-free water.
One requirement of a filtration method imposed by the physics involved is a measurable pressure drop through the filter bed, which restricts the rate of flow and sometimes requires the application of external pressure to force the liquid through the filter at a practical flow rate. In addition, to achieve the contact time required for complete reaction, conventional filters tend to be disposed with large volumes of filter medium. More compact filters, incorporating a smaller volume of active ingredient require a slower water flow rate to maximize contact time and, therefore, optimize chlorine removal.
Another disadvantage of filtration systems relates to biological contamination of the filter bed. Potable water, however clean, always carries some microorganisms, including bacteria. Filtration devices using activated carbon remove not only chlorine but also other organic and inorganic components found in water. These components serve as nutrients for bacteria and other microorganisms in the water. Because these filters usually retain water during periods of non-use, they provide ideal environments for growth of waterborne bacteria on the nutrients that have been accumulated in the filter bed. During periods of non-use of the filter, the bacteria and other microorganisms multiply rapidly within the filter material until they are flushed out during the next use of the device. Following a period of non-use, the first sample of water to pass through the filter will usually be heavily laden with bacteria. Incorporation of a filtration system in a device which is used intermittently, for example an automatic coffee maker, will expose the user to such bacterial contamination. Even if the bacteria are destroyed by subsequent heating of the water, as might occur in the automatic coffee maker, a variety of toxic products are released from the bacterial cells during their destruction and these harmful bacterial byproducts will be in the water used for the beverage.